1. Field of the Invention
The present invention relates to a linear motion guide unit having wide application in sliding parts incorporated in, for example, semiconductor manufacturing equipments, various assembling machines, numerical control (NC) processors, measurement/testing instruments, and so on. More particularly, it relates to a linear motion guide unit in which a slider is forced to move lengthwise relative to a track rail.
2. Description of the Prior Art
Linear motion guide units have been universally recognized for fundamental and versatile means to more encourage the recently remarkable growth of mechatronics. Although the linear motion guide units have been extensively built in machinery in fields as diverse as semiconductor manufacturing equipments, a variety of assembling machines, numerical control (NC) processors, measurement/testing instruments, and so on, the expansion of uses accompanied by the current developments in advanced technologies requires more and more such linear motion guide units that can manage growing demands for shrinkage in size, weight reduction, high precision, low-frictional resistance, high-speed moving, easy assemblage, versatility and the like.
There is conventionally known a linear motion guide unit of the sort disclosed in, for example Japanese Utility Model Laid-Open No. 37621/1987, which is a co-pending application filed by the present assignee. With the prior linear motion guide unit in which a table fits for linearly sliding movement in a guide way made of a thin steel material formed in an U-shape in cross section, there are provided stoppers to keep the moving table against getting out of the guide way. The stoppers are provided by forward and aft bent ends of the guide way as shown in FIG. 1 of the document referred to earlier. The moving table could be protected from any runaway out of the guide way after any one of forward and aft end caps on the moving table has come in abutment against the associated stopper. Should the table get out of the guide way, rolling elements would fall apart from one another. As an alternative shown in FIG. 4 of the reference document, the stoppers of tiny plate are secured with fastening screws on forward and aft ends of the guide way, one to each end. With this alternative, the table is also made to come in engagement at any one of its forward and aft ends with the associated stopper as shown in FIG. 5 of the reference document. Besides, this alternative is made in such construction that the rolling elements are not allowed to run in recirculating way.
With the prior stopper stated earlier to keep the table against getting out of the guide way of the thin steel member formed in an U-shape in cross section, however, it is needed to go to the trouble of making any extra part that should be bent. The table would be hard to fit in the guide way, once the extra parts got bent to provide the stoppers. The alternative stopper of tiny plate secured with fastening screws on the guide way needs a number of parts, and therefore takes up relatively much space. In contrast, the advanced technology looks to shrink the stopper down to make the linear motion guide unit compact in construction.
In Japanese Patent No. 2948944, which is also a co-pending application filed by the present assignee, another sort of linear motion guide unit is disclosed, in which any one of members confronting one another for sliding relative movement, as shown in FIG. 1 of the reference document is made therein with a lengthwise slot while the other has a stopper pin extending to fit in the slot. This prior construction allows leaving any specific stopper mechanism out of the linear motion guide unit. Since the stopper construction for the linear motion guide unit referred to earlier needs to cut the lengthwise slot in the fixed second member, however, it would be very tough to cut the lengthwise slot in a guide rail slim in thickness or make the stopper construction extending across the entire width of the linear motion guide unit. This means that this prior stopper construction is applicable to large linear motion guide units, but hardly suited for small guide unit especially slim or thin in thickness.
Japanese Utility Model Laid-Open No. 130017/1982, which is also a co-pending application filed by the present assignee, discloses another linear motion guide unit of cross-roller way type, in which rolling elements, as shown in FIGS. 1 and 2 of the reference document, are allowed to roll over only a definite travel instead of rolling through a recirculating circuit. This linear motion guide unit is mainly composed of a bed, table, and guide rails for the bed and the table, all of which are made of steel material. As seen from FIG. 1 of the reference document where the table is partially cut away, a stopper is constituted with first bolts fastened inside the table at the widthwise middle near forward and aft ends of the table, and a second bolt fastened on the upper surface of the guide rail for the bed midway between the first bolts inside the table so as to come in collision against the first bolts. The stopper in the linear motion guide unit of cross-roller way type recited earlier, because of being constituted with just bolts, is simple in construction, but needs much space to fasten the bolts underneath the table. Thus, this prior stopper construction would be also suited for only the relatively large linear motion guide units.
In Japanese Patent Laid-Open No. 200363/1996 there is disclosed lubricating means for the linear motion guide unit in which the track rail has no stopper construction to have the slider come to rest at any lengthwise end of the guide rail. This prior disclosure, although doing with the linear motion guide unit made smaller in construction, but does not involve technical concept about how to install the stopper construction to get the slider come to rest at any lengthwise end of the guide rail. The stopper construction, if necessary, may be as simple as any tentative stoppers extending between the raceway grooves at the lengthwise ends of the guide rail.
With linear motion guide unit to be made shrunken in size and compact in construction where both the slider and the guide rail are made slim or thin in thickness, it still remains a major challenge to realize how to provide a stopper construction to keep a slider against getting out of the guide way, especially, protecting the small rolling elements against falling apart from one another, which would occur when the slider became untethered from the guide rail while on a linear movement.